Modelling Polycrystalline Materials: An Overview of Three-Dimensional Grain-Scale Mechanical Models

International audienc

Large-scale 3D random polycrystals for the finite element method: Generation, meshing and remeshing

International audienceA methodology is presented for the generation and meshing of large-scale three-dimensional random polycrystals. Voronoi tessellations are used and are shown to include morphological properties that make them particularly challenging to mesh with high element quality. Original approaches are presented to solve these problems: (i) "geometry regularization", which consists in removing the geometrical details of the polycrystal morphology, (ii) "multimeshing" which consists in using simultaneously several meshing algorithms to optimize mesh quality, and (iii) remeshing, by which a new mesh is constructed over a deformed mesh and the state variables are transported, for large strain applications. Detailed statistical analyses are conducted on the polycrystal morphology and mesh quality. The results are mainly illustrated by the high-quality meshing of polycrystals with large number of grains (up to 105), and the finite element method simulation of a plane strain compression of ε = 1.4 of a 3000-grain polycrystal. The presented algorithms are implemented and distributed in a free (open-source) software package: Neper

Analyses numériques des conséquences mécaniques de transformation de phase diffusionnelle dans l'acier: plasticité de transformation et effet de pré-écrouissage

Afin de tenter de rendre compte correctement de l'effet -expérimentalement observé- d'une pré-charge de la phase austénitique sur la plasticité induite par transformation diffusionnelle dans un acier, nous avons développé 3 modélisations basées sur l'approche par EF, se différenciant essentiellement par la cinétique de germination imposée dans ces modélisations. Ce travail propose tout d'abord une analyse de l'effet de pré-charge de la phase parente sur la plasticité de transformation dans le cas d'un domaine d'étude réduit à une cellule contenant un germe en son centre. Puis est présentée la nouvelle approche où des germes apparaissent aléatoirement dans l'espace et dans le temps selon une loi de distribution donnée. Cette approche, outre le fait qu'elle est basée sur une cinétique de transformation cohérente par rapport à la métallurgie, a pour but de fournir des résultats sensibles aux paramètres contrôlant la germination

Coronary and contractile effects of intracoronary bradykinin and their modulation by ACE inhibitor in normal conscious dogs

为满足各种各样的应用程序的需求,EJB容器的服务框架必须能支持各种服务的集成.该文给出了一个EJB容器的可扩展服务框架的设计和实现.该EHB容器允许服务以Interceptor的方式加入容器.当EJB容器发生函数调用等事件时,容器自动触发这些相应的服务,从而能实现透明地在EJB容器中添加额外的服务

Plasticité induite par transformation de phase martensitique dans l’acier 35NCD16

Cette étude porte sur la plasticité des aciers au cours d'une transformation de phase martensitique. Nous nous intéressons à la Plasticité Induite par la Transformation (Transformation Induced Plasticity ou TRIP), dans l’acier 35NCD16. Différents types d’essais ont été réalisés pour mettre en évidence ce phénomène sous diverses conditions de chargement uniaxial en cours de transformation (constant, linéaire croissant, linéaire décroissant…). En effet, classiquement les essais de TRIP sont réalisés sous un chargement constant durant toute la transformation ce qui n’est pas forcément représentatif des conditions de sollicitations réelles dans les structures industrielles. Les prédictions des modèles de Leblond (1989) et de Taleb et Sidoroff (2003) pour ces essais feront l’objet d’une discussion

Small variable segments constitute a major type of diversity of bacterial genomes at the species level.

International audienceBACKGROUND: Analysis of large scale diversity in bacterial genomes has mainly focused on elements such as pathogenicity islands, or more generally, genomic islands. These comprise numerous genes and confer important phenotypes, which are present or absent depending on strains. We report that despite this widely accepted notion, most diversity at the species level is composed of much smaller DNA segments, 20 to 500 bp in size, which we call microdiversity. RESULTS: We performed a systematic analysis of the variable segments detected by multiple whole genome alignments at the DNA level on three species for which the greatest number of genomes have been sequenced: Escherichia coli, Staphylococcus aureus, and Streptococcus pyogenes. Among the numerous sites of variability, 62 to 73% were loci of microdiversity, many of which were located within genes. They contribute to phenotypic variations, as 3 to 6% of all genes harbor microdiversity, and 1 to 9% of total genes are located downstream from a microdiversity locus. Microdiversity loci are particularly abundant in genes encoding membrane proteins. In-depth analysis of the E. coli alignments shows that most of the diversity does not correspond to known mobile or repeated elements, and it is likely that they were generated by illegitimate recombination. An intriguing class of microdiversity includes small blocks of highly diverged sequences, whose origin is discussed. CONCLUSIONS: This analysis uncovers the importance of this small-sized genome diversity, which we expect to be present in a wide range of bacteria, and possibly also in many eukaryotic genomes

Analysis by x-ray microtomography of a granular packing undergoing compaction

Several acquisitions of X-ray microtomography have been performed on a beads packing while it compacts under vertical vibrations. An image analysis allows to study the evolution of the packing structure during its progressive densification. In particular, the volume distribution of the pores reveals a large tail, compatible to an exponential law, which slowly reduces as the system gets more compact. This is quite consistent, for large pores, with the free volume theory. These results are also in very good agreement with those obtained by a previous numerical model of granular compaction.Comment: 4 pages, 4 figures. Latex (revtex4). to be published in Phys. Rev.

Cytonuclear interactions remain stable during allopolyploid evolution despite repeated whole-genome duplications in Brassica

Several plastid macromolecular protein complexes are encoded by both nuclear and plastid genes. Therefore, cytonuclear interactions are held in place to prevent genomic conflicts that may lead to incompatibilities. Allopolyploidy resulting from hybridization and genome doubling of two divergent species can disrupt these fine-tuned interactions, as newly formed allopolyploid species confront biparental nuclear chromosomes with a uniparentally inherited plastid genome. To avoid any deleterious effects of unequal genome inheritance, preferential transcription of the plastid donor over the other donor has been hypothesized to occur in allopolyploids. We used Brassica as a model to study the effects of paleopolyploidy in diploid parental species, as well as the effects of recent and ancient allopolyploidy in Brassica napus, on genes implicated in plastid protein complexes. We first identified redundant nuclear copies involved in those complexes. Compared with cytosolic protein complexes and with genome-wide retention rates, genes involved in plastid protein complexes show a higher retention of genes in duplicated and triplicated copies. Those redundant copies are functional and are undergoing strong purifying selection. We then compared transcription patterns and sequences of those redundant gene copies between resynthesized allopolyploids and their diploid parents. The neopolyploids showed no biased subgenome expression or maternal homogenization via gene conversion, despite the presence of some non-synonymous substitutions between plastid genomes of parental progenitors. Instead, subgenome dominance was observed regardless of the maternal progenitor. Our results provide new insights on the evolution of plastid protein complexes that could be tested and generalized in other allopolyploid species

X-Ray Detected Magnetic Resonance: A Unique Probe of the Precession Dynamics of Orbital Magnetization Components

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy in which X-ray Magnetic Circular Dichroism (XMCD) is used to probe the resonant precession of local magnetization components in a strong microwave pump field. We review the conceptual bases of XDMR and recast them in the general framework of the linear and nonlinear theories of ferromagnetic resonance (FMR). Emphasis is laid on the information content of XDMR spectra which offer a unique opportunity to disentangle the precession dynamics of spin and orbital magnetization components at given absorbing sites. For the sake of illustration, we focus on selected examples in which marked differences were found between FMR and XDMR spectra simultaneously recorded on ferrimagnetically ordered iron garnets. With pumping capabilities extended up to sub-THz frequencies, high-field XDMR should allow us to probe the precession of orbital magnetization components in paramagnetic organometallic complexes with large zero-field splitting. Even more challenging, we suggest that XDMR spectra might be recorded on selected antiferromagnetic crystals for which orbital magnetism is most often ignored in the absence of any supporting experimental evidence

La confiance mutuelle dans l'espace pénal européen/Mutual Trust in the European Criminal Area

L'ouvrage constitue une réflexion approfondie sur la problématique de la confiance mutuelle dans l'espace pénal européen, un thème d’une brûlante actualité dès lors que l'importance de la confiance mutuelle dans cet espace va croissant